This invention relates generally to the art of visual displays and similar light-control devices and relates more particularly to liquid crystal displays which incorporate an azine compound as part of the system for selective transmission of visible light.
Organic substances which exhibit a mesophase have been known for many years, but it has been only more recently that the technology of liquid crystal materials has been developed sufficiently to achieve commercial application in such devices as wrist watches and digital readouts.
The substances which exhibit a liquid crystal phase, as postulated by Gray and Harrison in U.S. Pat. No. 3,947,374 for example, comprise a molecule with a central linkage group and a pair of distal chemical groups of varying character. These patentees recognize the prior utility of Schiff Bases and themselves disclose commercially useful liquid crystal properties for certain biphenyl compounds. Gray and Harrison also teach that the presence of an unsaturated group in the linkage unit is associated with undesirable, chemical and/or photochemical instability. In addition, Kmetz and Willisen in "Nonemissive Electrooptic Displays," Plenum Press, New York and London (1976), have suggested possible display performance for azine compounds with identical distal groups, although the authors admit that almost nothing is known about the properties of liquid crystal azine compounds.